Starting and operating circuit for electric discharge devices



April 18, 1950 B. N. cLAcK ET AL STARTING AND OPERATING CIRCUIT FDR ELECTRIC DISCHARGE DEVICES Filed May 10,

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Patented Apr. 18, 1950 STARTING AND. OPERATING CIRCUITFOR- ELECTRIGDISCHARGE DEVIQES Basil Noel "Clack, :Wembley Park, and Douglas Shepherd .Hills,-1'Kenton,- England, assignors to General Elect ic Comp ny, a. corporation of Application May 10, 1948, Serial No.*26,154 In Great Britain May 14, 1947 .1 Claim. -1

This invention relates to electrical discharge devices of the type employing ionizable. mediums such as gases or vapors, and more particularly to starting and operatingcircuits therefor.

"The present invention relates more particularly to electric 'discharge lamp circuits of'the type comprising an operating or discharge circuit embodying a choke-or inductive ballast in series with a lamp across a source of alternating current supply and a starting circuit in parallel with the lamp and embodying a capacitance connected in series with a glowdischarge device. The glow discharge-device or switch is designed to close on the initial applicationof-the current supply to the discharge circuit and to open upon conduction of the lamp. The values ofthe inductive ballast and the capacitance are: such that when the-glow switch is closed they form together a resonant or partially resonant circuit having a resonance frequency between a frequency approximate to that of the supplyvoltage and three times its value. With suchanarrangement the initial voltage across the lamp is relatively large and isarranged tobe suilicient to cause an arc discharge to occur between the electrodes of the lamp. When-an arc discharge occurs, the voltage drop across the lamp decreases and in turn the voltage drop across the glow switch @decreases so that the switch.isextinguished, thus disconnecting the capacitance from the operating circuit and eliminating the resonant condition.

In some installations, howevena disadvantage has been noted in that the peak voltage appearing across the glow'swi-tchwhen the discharge lamp is normally'conductive exceeds the extinguishing voltage of the glow switch. Thus, the glow switch does not remain open and the starting circuit remains continually energized.

An object of our invention is to provide a new and improved circuit for starting and operating electrical discharge devices.

Another object of our invention is to provide a new and improved means for impressing a starting voltage across the electrodes of an electric discharge device and effectively removing the starting voltage during operation of the electric discharge device.

A further object of our invention is to provide a new and improved means of rendering a glow switch, used in a series resonant starting circuit for starting an electrical discharge device, inoperative upon conduction of the electrical discharge device even though the peak voltage oc curring across the electrical discharge device exceeds the extinguishing voltage of the .glow

switch.

Further featuresaand advantages. of; our; 'lnven tion will appear from the.followingdescriptiop of species thereof.

For a better .understandingof ourinvention reference may behadto the following description taken in connection with the accompanying drawing and its scope willbe pointed out; in the with oxides; of alkaline earth metals, :such .as,:.a mixture of barium or strontium oxides. Thetenvelope 5 2 contains. a. gaseous atmosphere, such .as av rare gas like neon, .argonormixtures thereof at a. pressure of. a1few-.millimetersrand. a. small quantity of mercury which, during the operation of..the. lamp, has .a low...pr.essure of the; orderaof 10. microns. :The device.- I may. be alow. pressure positive. column lam-p .of .a. fluorescent type-mmvided with a suitable phosphor or fluorescent coating. This fluorescent coating .npcni excitationzby the radiation producedbyan electric discharge between the electrodes, transforms ;;;a

.shorterwave radiation duezto dischargeiainto longer wave radiation such as radiation within the visible range. For ease of starting a stripe or strip 5 of conductive material which, for exam- :ple, may be a metallic paint or graphite mixed with potassium silicate, may be applied to the surface of device I. The starting strip 5 may be connected to one or both of the electrodes.

In accordance with our invention the lamp l is connected through input terminals 6, 6 across a suitable power supply circuit which, for example, may be 118 volt, cycle source, for supplying current t lamp I through the usual ballast I which serves as a starting inductance and is connected in a series circuit between one of the input terminals 6, 6' and one of the output terminals l0, Ill. A manual make-and-break control switch 8 may be used to connect lamp I to the power supply. A parallel starting circuit 9, 9 including a capacitance I0 connected in series with a glow discharge switch H, and an impedance element l2 shunts lamp I. A second impedance element I3 is connected across and shunts the glow-switch H. The values of the inductive ballast and the capacitance are such that when the glow switch is closed they form together a resonant or partially resonant circuit having a resonance frequency between a frequency approximate to that of the supply voltage and three times this frequency. For purposes of our application, a partial resonant circuit is one which provides a voltage substantially larger than the supply voltage but has a resonance frequency differing from that of the supply voltage, or from a harmonic thereof. The values of impedance elements 12 and I3 which, for example, may be pure resistances, are such as to prevent glow switch H from closing when the discharge lamp or device I is conducting.

' Glow-switch II, for example, may comprise a glass bulb i4 filled with a rare gas, such as neon or argon, a U-shaped bimetallic strip l5, and a fixed contact or electrode It. When current flows through starting circuit 9, =9 a'glow is produced in switch II which actuates the bimetallic strip [5 until it contacts the fixed contact or electrode IS. The glow discharge is extinguished by the bimetallic strip contacting the electrode l5 and'thus the bimetal cools and in 'a very short time the contacts formed by bimetallic strip I5 and electrode 16 disengage each other.

When the entire installation is energized by closing switch 8,'current flows through the ballastl, capacitive reactance I0, glow switch ll,

of. The impedance elements I2 and I3 modify the waveform of the voltage in such a manner that the glow switch H remains open thereafter during conduction of lamp I. This is ensured by arranging that once the glow switch II has opened the current flowing through impedance v elements "I 2 and I3 and capacitance I0 is such that the voltage appearingacross the impedance element l3 and hence the glow switch I I, is below the striking voltage of glow'switch l I.

' In one working example of our invention the stabilizing choke or ballast had a value of 0.8 henry, the capacitance 2 microfarads, resistance l2 had a value of 200 ohms and resistance l3 shunting the glow discharge: device had a resistance of one megohm. These circuit constants were used with a supply voltage having a frequency of 50 cycles per second. It will be observed from the above values that the resistance 12 is small in comparison with the impedance of the capacitance ID at the frequency of the supply, and that the resistance 13 is large in comrparisonwith the impedance of the capacitance ID at the frequency of the supply.

What we claim as new and desire to secure by Letters Patent of the United States is: A circuit for starting and operating a gaseous electric discharge lamp having electrodes spaced apart in a sealed envelope, comprising input terminals for connection to a source of alternating current supply of predetermined voltage and frequency and output terminals for connection to the discharge lamp, a series circuit including'a ballasting inductance connected between aninput and an output terminal, and a parallel circuit including a capacitance, a glow switch and a first resistance all connected in series across said output terminals and a second resistance connected across said glow switch, the values of the inductance and the capacitance being such' that when the glow switch is closed they form a resonant circuit, said glow switch having an ionizing potential less than the maximum voltage across said lamp when conducting, and said first and second resistances having values respectively smaller and larger than the reactance of said capacitance at said frequency in order to reduce the potential across said glow switch, when said lamp is conducting, to a figure less than the ionizing potential of said switch, without destroying the resonant condition of said circuit whenever said glow switch is closed.

BASIL NOEL CLACK.

DOUGLAS SHEPHERD HILLS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS v 7 Date 

